SRF CONTROLLED DVR FOR COMPENSATION OF BALANCED AND UNBALANCED VOLTAGE DISTURBANCES

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International Journal of Electrical Engineering & Technology (IJEET)

Volume 7, Issue 3, May–June, 2016, pp.73–92, Article ID: IJEET_07_03_007

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SRF CONTROLLED DVR FOR

COMPENSATION OF BALANCED AND

UNBALANCED VOLTAGE DISTURBANCES

SYED SURAYA

Research Scholar,

Electrical & Electronics Engineering,

JNTUA, Ananthapuramu, AP, India

Dr. K.S.R.ANJANEYULU

Professor in Electrical & Electronics Engineering,

JNTUA, Ananthapuramu,AP, India

ABSTRACT

The growth of power electronic technology in the field of electric power

sector has caused a greater awareness on the power quality of distribution

systems. With the re-structuring of power systems and with shifting trend

towards distributed and dispersed generation, the issue of power quality is

going to take newer dimensions. The present research is to identify the

prominent concerns in this area and hence the measures that can enhance the

quality of power. This paper investigates the problems of voltage sag, swell

and its severe impact on nonlinear loads, sensitive loads. Protection of the

sensitive unbalanced nonlinear loads from sag/swell, distortion, and

unbalance in supply voltage is achieved economically using the dynamic

voltage restorer (DVR).DVR is installed between supply and load which will

inject voltage and active power to the distribution system during

balanced/unbalanced voltage sag and swell disturbances. The control

technique used to operate the DVR is SRF Theory with Proportional Integral

(PI) controller. The performance of DVR based Synchronous reference frame

theory (SRF) for the mitigation of voltage sag, swell for balanced and

unbalanced voltages is tested and Simulation results are carried out by

MATLAB with its Simulink to analyze the proposed method.

Key words: Synchronous Reference Frame Theory (SRF), Balanced and Un

Balanced Voltage, Dynamic Voltage Restorer (DVR).

Syed Suraya and Dr. K.S.R.Anjaneyulu


Cite this Article: Syed Suraya and Dr. K.S.R.Anjaneyulu, SRF Controlled

DVR for Compensation of Balanced and Unbalanced Voltage Disturbances.

International Journal of Electrical Engineering & Technology, 7(3), 2016, pp.

73–92.

http://www.iaeme.com/ijeet/issues.asp?JType=IJEET&VType=7&IType=3

1. INTRODUCTION

In power distribution systems the advent of a large numbers of sophisticated electrical

and electronic equipment such as computers, programmable logic Controllers and

variable speed drives causes various power quality problems like voltage sag, voltage

swell and harmonics. These are the major concern of the industrial and commercial

electrical consumers due to enormous loss in terms of time and money, in which

voltage sag and swell are major power quality problems [1].

Voltage sags and swells are the most common power quality problems in

electrical distribution systems. Voltage sag is defined as decrease in the rms value of

voltage magnitude. Voltage swell is defined as increment in the rms value of voltage

magnitude. There are two types of voltage sag and swell which can occur on any

transmission lines; balanced and unbalanced voltage sag and swell which are also

known as symmetrical and asymmetrical voltage sag and swell respectively. Most of

these faults that occur on power systems are not the balanced three-phase faults, but

the unbalanced faults. In the analysis of power system under fault conditions, it is

necessary to make a distinction between the types of fault to ensure the best results

possible in the analysis. In balanced voltage sag & swell, voltage decreases and

increase in all three phases simultaneously. In unbalanced voltage sag & swell voltage

decrease and increases in only one phase or two phases at a time [2].

Custom power devices are used to compensate these power quality problems in

the systems. There are different types of Custom power devices used in electrical

network to improve power quality problems. Each of the devices has its own benefits

and limitations. A few of these reasons are as follows. The SVC (Static Var

Compensator) pre-dates the DVR, but the DVR is still preferred because the SVC has

no ability to control active power flow [3][4]. Another reason include that the DVR

has a higher energy capacity compared to the SMES (Super Conducting Magnetic

Energy Storage) and UPS devices. Furthermore, the DVR is smaller in size and cost is

less compared to the DSTATCOM (Distributed Static Compensator) and other custom

power devices. Based on these reasons, it is no surprise that the DVR is widely

considered as an effective custom power device in mitigating voltage sags. In addition

to voltage sags and swells compensation, DVR can also add other features such as

harmonics and power factor correction. Compared to the other devices, the DVR is

clearly considered to be one of the best economic solutions for its size and capabilities

[5].Dynamic Voltage Restorer is located between grid and sensitive load. It injects

controlled voltage to keep dc link voltage constant at load-side.

The proposed DVR is connected to the system through the three single phase

injection transformers. DVR is designed according to the voltage needed in the

secondary side of transformer. The DVR consists of three single phase VSI units.

Each unit is connected to system through the injection transformer. It provides the

isolation to the converter.[6]

The performance of DVR depends up on control strategy used. In this paper SRF

Theory with Proportional Integral (PI) controller technique is used for compensation

of balanced/unbalanced voltage sag and swell. The generation of Vd ,Vq and Vo

SRF Controlled DVR For Compensation of Balanced and Unbalanced Voltage Disturbances


reference signal involves the conversion from three-phase to two-phase and vice

versa. Moreover low pass filters are essential part of this algorithm which has slow

dynamic response of the compensator.[7],[8]

The paper is organized as follows. In section 2, the configuration part of the DVR

is described, the Control technique and the voltage injection capabilities of the DVR

is discussed in section 3, and the detailed description of MATLAB Simulation model

along with its performance in electrical network is discussed in section 4.

2. DYNAMIC VOLTAGE RESTORER (DVR) CONFIGURATION

DVR is a Custom Power Device used to eliminate supply side voltage disturbances.

DVR also known as Static Series Compensator maintains the load voltage at a desired

magnitude and phase by compensating the voltage sags/swells and voltage unbalances

presented at the point of common coupling. The power circuit of the DVR is shown in

Fig. 1.

Vsa

Vsb

Vsc

LS

LS

LS

Vsa

Vsb

Vsc

Vdvra

Vdvrb

Vdvrc

Lse Lse Lse

Vt

CseCse Cse

Sensitive

Load

1T3T

4T2T6T

5T

SRF THEORY FOR

UNBALANCED CONDITION

Gate Pulses

Energy

Storage

VSabc

LC Filters

Injection

TransFormer

Voltage Source

Converter

GRID

Figure 1 DVR Block Diagram

The DVR consists of the following major parts:-

Voltage Source Inverter (VSI)

PWM inverter using IGBT switches is used in the model. IGBT switches are

commonly used in series connected circuits. The insulated gate bipolar transistor or

IGBT is a three-terminal power semiconductor device, noted for high efficiency and

fast switching. Pulse-width modulation (PWM) is a very efficient way of providing

intermediate amounts of electrical power between fully on and fully off. The voltage

source converter is used to convert the DC to AC and then supply the voltage to

distribution feeder through an injection transformer.



Injection Transformers

The injection transformers connect the DVR to the distribution network via the high

voltage windings. They transform and couple the injected compensating voltages

generated by the VSI to the incoming supply voltage. Basically injection transformers

used in the model presented in this paper are three single phase transformers. The

high voltage side of the injection transformer is connected in series to the distribution

line, while the low voltage side is connected to the DVR power circuit. For a three-

phase DVR, three single-phase or three-phase voltage injection transformers can be

connected to the distribution line, and for single phase DVR one single-phase

transformer is connected. The transformers not only reduce the voltage requirement of

the inverters, but also provide isolation between the inverters.

Passive Filters

Passive filters are placed at the high voltage side of the DVR to filter the harmonics.

These filters are placed at the high voltage side as placing the filters at the inverter

side introduces phase angle shift which can disrupt the control algorithm.

Energy storage

The energy storage unit supplies the required power for compensation of load voltage

during voltage sag. A dc battery is used for this purpose. Batteries, flywheels or SMEs

can be used to provide real power for compensation. Compensation using real power

is essential when large voltage sag occurs.

3. DVR CONTROLLING BASED ON SYNCHRONOUS

REFERENCE FRAME THEORY

The following figure shows the Control Block Diagram of the DVR .In this control,

Source Voltage is sensed and is given as an input to the abc/dq transformation block

.The same source voltage is given as an input to the PLL block , this PLL block gives

the information of sin, cos .This is given as an input to the abc/dq block, with these

two inputs this transformation block gives Vd, Vq, and Vo information .This

information is compared with Vdact, Vqact and Voact which are the actual

parameters .The quadrature and Vo axis is compared with 0 p.u .The error generated

is given as an input to the pi controller ,the pi controller output is again given as an

input to dq/abc block , and PLL information is also given as an input to dq/abc block.

This block gives us the pulse information which is given as an input to pwm generator

and from that gate pulses are generated, those gate pulses are for inverter.



PLL

VSabc

dq0

Vdref

VdactVd

Vq

PI

PI

Vqref

Vqact

VSabc

1 P.U

P.U0

dq0

abc

PWM

GeneratorGate

Pulses

Sin(wt),cos(wt)Vo

PI

Vo ref

Vo act

P.U0

abc

Figure 2 DVR Control Block Diagram based on SRF Theory

4. MATLAB/SIMULATION RESULTS AND DISCUSSION

The performance of the DVR is demonstrated for different supply voltage

disturbances such as balanced and unbalanced sag and swells at terminal voltages.

The DVR is modelled and simulated using the MATLAB and its Simulink.

Case 1: Balanced Sag Condition

Figure 3 Matlab/Simulink model with DVR for BalancedSag Condition



Figure 4 DVR Final Sag Case (a) Source Voltage (b) DVR Voltage(c) Load Voltage

Fig.4 Shows the Balanced Sag condition of a DVR .In Supply Voltage Sag occurs

at period 0.1 and continues upto 0.2.In this period i.e from 0.1 to 0.2 DVR injects the

Compensation Voltage and load side voltage is maintained constant.

Case: 2 Balanced Swell Condition

Figure 5 Matlab/Simulink model with DVR for Balanced Swell condition



Figure 6 DVR Final Swell case (a) Source Voltage (b) DVR Voltage(c) Load Voltage

Fig.6 Shows the Balanced Swell condition of a DVR .In Supply Voltage Swell

occurs at period 0.1 and continues up to 0.2.In this period i.e from 0.1 to 0.2 DVR

injects the Compensation Voltage and load side voltage is maintained constant.

Case 3: Balanced Multiple Sag Condition

Figure 7 Matlab/Simulink model with DVR for BalancedMultiple Sag Condition



Figure 8 DVR Final Multiple Sag case (a) Source Voltage (b) DVR Voltage(c) Load Voltage

Fig.8 Shows the Balanced Multiple Sag condition of a DVR .In Supply Voltage

Sag occurs at period 0.1 and continues upto 0.2, and 0.25 to 0.35 .In this period i.e

from 0.1 to 0.2 and 0.25 to 0.35 DVR injects the Compensation Voltage and load side

voltage is maintained constant.

Case 4:Balanced Multiple Swell Condition

Figure 9 Matlab/Simulink model with DVR for BalancedMultiple Swell Condition



Figure 10 DVR Final Multiple Swell case (a) Source Voltage (b) DVR Voltage (c) Load

Voltage

Fig.10 Shows the Balanced Multiple Swell condition of a DVR .In Supply

Voltage Swell occurs at period 0.1 and continues up to 0.2, and 0.25 to 0.35 .In this

period i.e from 0.1 to 0.2 and 0.25 to 0.35 DVR injects the Compensation Voltage and

load side voltage is maintained constant.

Case 5: Balanced Sag and Swell Condition

Figure 11 Matlab/Simulink model with DVR for BalancedSag and Swell Condition



Figure 12 DVR Final Multiple Swell case (a) Source Voltage (b) DVR Voltage (c) Load

Voltage

Fig.12 Shows the Balanced Sag and Swell condition of a DVR .In Supply Voltage

Sag occurs at period 0.1 and continues up to 0.2, and Swell occurs at 0.25 to 0.3 .In

this period i.e from 0.1 to 0.2 and 0.25 to 0.3 DVR injects the Compensation Voltage

and load side voltage is maintained constant.

Case 6: Single Phase Sag Condition

Figure 13 Matlab/Simulink model with DVR for Single Phase Sag Condition



Figure 14 DVR Single Phase Sag case (a) Source Voltage (b) DVR Voltage (c) Load Voltage

Fig.14 Shows the Single Phase Sag condition of a DVR .In Supply Voltage Sag

occurs at period 0.1 and continues upto 0.2 in a Single Phase. In this period i.e from

0.1 to 0.2 DVR injects the Compensation Voltage and load side voltage is maintained

constant.

Case 7: Two Phase Sag Condition

Figure 15 Matlab/Simulink model with DVR for Two Phase Sag Condition



Figure 16 DVR Two Phase Sag case (a) Source Voltage (b) DVR Voltage (c) Load Voltage

Fig.16 Shows the Two Phase Sag condition of a DVR .In Supply Voltage Sag

occurs at period 0.1 and continues upto 0.2 in a Two Phase. In this period i.e from 0.1

to 0.2 DVR injects the Compensation Voltage and load side voltage is maintained

constant.

Case 8: Unbalanced Sag Condition

Figure 17 Matlab/Simulink model with DVR for Unbalanced Sag Condition



Figure 18 DVR Unbalanced Sag case (a) Source Voltage (b) DVR Voltage (c) Load Voltage

Fig.18 Shows the Unbalanced Sag condition of a DVR .In Supply Voltage Sag

occurs at period 0.1 and continues upto 0.2 in a Two Phase. In this period i.e from 0.1

to 0.2 DVR injects the Compensation Voltage and load side voltage is maintained

constant.

Case 9: Unbalanced Multiple Sag Condition

Figure 19 Matlab/Simulink model with DVR for Unbalanced Multiple Sag Condition



Figure 20 DVR Unbalanced Sag case (a) Source Voltage (b) DVR Voltage (c) Load Voltage

Fig.20 Shows the Unbalanced Multiple Sag condition of a DVR .In Supply

Voltage Sag occurs at period 0.1 and continues upto 0.2, and 0.3 to 0.4 .In this period

i.e from 0.1 to 0.2 and 0.3 to 0.4 DVR injects the Compensation Voltage and load side

voltage is maintained constant.

Case 10: Single Phase Swell Condition

Figure 21 Matlab/Simulink model with DVR for Single Phase Swell Condition



Figure 22 DVR Single Phase Swell case (a) Source Voltage (b) DVR Voltage (c) Load

Voltage

Fig.22 Shows the Single Phase Swell condition of a DVR .In Supply Voltage

Swell occurs at period 0.1 and continues upto 0.15 in a Single Phase. In this period i.e

from 0.1 to 0.15 DVR injects the Compensation Voltage and load side voltage is

maintained constant.

Case 11: Two Phase Swell Condition

Figure 23 Matlab/Simulink model with DVR for Two Phase Swell Condition



Figure 24 DVR Two Phase Swell case (a) Source Voltage (b) DVR Voltage (c) Load Voltage

Fig.24 Shows the Two Phase Swell condition of a DVR .In Supply Voltage Swell

occurs at period 0.1 and continues upto 0.15 in a Two Phases. In this period i.e from

0.1 to 0.15 DVR injects the Compensation Voltage and load side voltage is

maintained constant.

Case 12: Unbalanced Swell Condition

Figure 25 Matlab/Simulink model with DVR for Unbalanced Swell Condition



Figure 26 DVR Unbalanced Swell case (a) Source Voltage (b) DVR Voltage (c) Load

Voltage

Fig.26 Shows the Unbalanced Swell condition of a DVR .In Supply Voltage Swell

occurs at period 0.1 and continues upto 0.2.In this period i.e from 0.1 to 0.2 DVR

injects the Compensation Voltage and load side voltage is maintained constant.

Case 13: Unbalanced Multiple Swell Condition

Figure 27 Matlab/Simulink model with DVR for Unbalanced Multiple Swell Condition



Figure 28 DVR Unbalanced Swell case (a) Source Voltage (b) DVR Voltage (c) Load

Voltage

Fig.28 Shows the Unbalanced Multiple Swell condition of a DVR .In Supply

Voltage Swell occurs at period 0.1 and continues upto 0.2, and 0.3 to 0.4 .In this

period i.e from 0.1 to 0.2 and 0.3 to 0.4 DVR injects the Compensation Voltage and

load side voltage is maintained constant.

Case 14: Unbalanced Sag and Swell Condition

Figure 29 Matlab/Simulink model with DVR for Unbalanced Sag and Swell Condition



Figure 30 DVR Unbalanced Sag and Swell case (a) Source Voltage (b) DVR Voltage

(c) Load Voltage

Fig.30 Shows the Unbalanced Sag and Swell condition of a DVR .In Supply

Voltage Sag occurs at period 0.1 and continues up to 0.2, and Swell occurs at 0.3 to

0.4. In this period i.e from 0.1 to 0.2 and 0.3 to 0.4 DVR injects the Compensation

Voltage and load side voltage is maintained constant.

5. CONCLUSION

The simulation analysis shows the performance of the DVR for compensating the

balanced/unbalanced voltage sag and swell in the distribution system.DVR is capable

of compensating the various voltage disturbances like single phase and two phase sag

and swell in unbalanced condition as well as sag and swell in unbalanced condition in

three phase. Various conditions are tested for the performance capability of DVR

through extensive simulation and results are verified.DVR is tested for balanced sag ,

swell, multiple sag and multiple swell and sag and swell cases, and in unbalanced

condition sag and swell in single and two phases as well as unbalanced three phase

condition. Matlab and Simulation results shows that the DVR is the best solution for

mitigating the various voltage disturbances in a distribution system.

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